gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2016 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "backend.h"
  24 #include "rtl.h"
  25 #include "tree.h"
  26 #include "df.h"
  27 #include "emit-rtl.h"
  28 #include "expr.h"
  29 #include "tree-pass.h"
  30
  31 /* Check all of the uses of pseudo variables.  If any use that is MUST
  32    uninitialized, add a store of 0 immediately before it.  For
  33    subregs, this makes combine happy.  For full word regs, this makes
  34    other optimizations, like the register allocator and the reg-stack
  35    happy as well as papers over some problems on the arm and other
  36    processors where certain isa constraints cannot be handled by gcc.
  37    These are of the form where two operands to an insn my not be the
  38    same.  The ra will only make them the same if they do not
  39    interfere, and this can only happen if one is not initialized.
  40
  41    There is also the unfortunate consequence that this may mask some
  42    buggy programs where people forget to initialize stack variable.
  43    Any programmer with half a brain would look at the uninitialized
  44    variable warnings.  */
  45
  46 static void
  47 initialize_uninitialized_regs (void)
  48 {
  49   basic_block bb;
  50   bitmap already_genned = BITMAP_ALLOC (NULL);
  51
  52   if (optimize == 1)
  53     {
  54       df_live_add_problem ();
  55       df_live_set_all_dirty ();
  56     }
  57
  58   df_analyze ();
  59
  60   FOR_EACH_BB_FN (bb, cfun)
  61     {
  62       rtx_insn *insn;
  63       bitmap lr = DF_LR_IN (bb);
  64       bitmap ur = DF_LIVE_IN (bb);
  65       bitmap_clear (already_genned);
  66
  67       FOR_BB_INSNS (bb, insn)
  68         {
  69           df_ref use;
  70           if (!NONDEBUG_INSN_P (insn))
  71             continue;
  72
  73           FOR_EACH_INSN_USE (use, insn)
  74             {
  75               unsigned int regno = DF_REF_REGNO (use);
  76
  77               /* Only do this for the pseudos.  */
  78               if (regno < FIRST_PSEUDO_REGISTER)
  79                 continue;
  80
  81               /* Ignore pseudo PIC register.  */
  82               if (pic_offset_table_rtx
  83                   && regno == REGNO (pic_offset_table_rtx))
  84                 continue;
  85
  86               /* Do not generate multiple moves for the same regno.
  87                  This is common for sequences of subreg operations.
  88                  They would be deleted during combine but there is no
  89                  reason to churn the system.  */
  90               if (bitmap_bit_p (already_genned, regno))
  91                 continue;
  92
  93               /* A use is MUST uninitialized if it reaches the top of
  94                  the block from the inside of the block (the lr test)
  95                  and no def for it reaches the top of the block from
  96                  outside of the block (the ur test).  */
  97               if (bitmap_bit_p (lr, regno)
  98                   && (!bitmap_bit_p (ur, regno)))
  99                 {
 100                   rtx_insn *move_insn;
 101                   rtx reg = DF_REF_REAL_REG (use);
 102
 103                   bitmap_set_bit (already_genned, regno);
 104
 105                   start_sequence ();
 106                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 107                   move_insn = get_insns ();
 108                   end_sequence ();
 109                   emit_insn_before (move_insn, insn);
 110                   if (dump_file)
 111                     fprintf (dump_file,
 112                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 113                              current_function_name (), regno, bb->index,
 114                              INSN_UID (insn));
 115                 }
 116             }
 117         }
 118     }
 119
 120   if (optimize == 1)
 121     {
 122       if (dump_file)
 123         df_dump (dump_file);
 124       df_remove_problem (df_live);
 125     }
 126
 127   BITMAP_FREE (already_genned);
 128 }
 129
 130 namespace {
 131
 132 const pass_data pass_data_initialize_regs =
 133 {
 134   RTL_PASS, /* type */
 135   "init-regs", /* name */
 136   OPTGROUP_NONE, /* optinfo_flags */
 137   TV_NONE, /* tv_id */
 138   0, /* properties_required */
 139   0, /* properties_provided */
 140   0, /* properties_destroyed */
 141   0, /* todo_flags_start */
 142   TODO_df_finish, /* todo_flags_finish */
 143 };
 144
 145 class pass_initialize_regs : public rtl_opt_pass
 146 {
 147 public:
 148   pass_initialize_regs (gcc::context *ctxt)
 149     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 150   {}
 151
 152   /* opt_pass methods: */
 153   virtual bool gate (function *) { return optimize > 0; }
 154   virtual unsigned int execute (function *)
 155     {
 156       initialize_uninitialized_regs ();
 157       return 0;
 158     }
 159
 160 }; // class pass_initialize_regs
 161
 162 } // anon namespace
 163
 164 rtl_opt_pass *
 165 make_pass_initialize_regs (gcc::context *ctxt)
 166 {
 167   return new pass_initialize_regs (ctxt);
 168 }